A breakdown in the insulation of an electrical cable, for example resulting in short-circuiting of a conductor and earth, can be a problem in any environment. Often, it is not sufficient simply to identify that such a fault has occurred, but also to determine the location of the fault. There are various techniques and devices available to do this. However, the problems are exacerbated when the cable is used in a remote or difficult to access location, where the use of such techniques or devices may not be easily practicable. Underwater fluid extraction facilities, for example subsea hydrocarbon extraction facilities, are examples of such remote locations.
Currently, the line isolation of subsea cables is measured to look for a breakdown of insulation to determine if a fault has occurred. With this information long term trends can be observed. This technique however does not provide information on the location of the fault on the cable. As mentioned above, at topside/surface parts of the facility this isn't a major problem, as commercial “off the shelf” cable fault detectors can be used. But for distributed systems e.g. involving communication electronics modules (CEMs) or power and communication distribution modules (PCDMs) etc, there is no easy way of knowing where the fault is on the subsea cable.
It is an aim of the present invention to overcome these problems and provide the location of insulation-breakdown faults on underwater cables simply and robustly.
This aim is achieved by the use of time domain reflectometry to locate the position of faults on a cable.
The present invention has particular application to umbilical cables connected to a distributed system of an underwater fluid extraction facility.
The invention would provide various advantages, for example it would enable an oil company to find precisely where a cable fault lies, so that they could then make an informed judgement on how to proceed, e.g. they could decide to investigate what caused the fault, such as fishing equipment, corrosion etc.